Several problems have heretofore been encountered when attempting to isolate metal atoms in a silicon substrate away from the active devices, commonly known as gettering. During manufacture of an integrated circuit, metal atoms often migrate into the silicon substrate when electronic components are assembled on the substrate. Unfortunately, during processing of the product, such metal atoms tend to migrate throughout the substrate. If a sufficient number of metal atoms migrate to the active device, the effectiveness of the integrated circuit can be significantly reduced. Problems caused by such metal atoms in the active device can range from electrical shorting of the integrated circuit to inadequate device performance due to reduced minority carrier lifetime.
In the past, gettering processes have been used in the integrated circuit industry to isolate or getter these metal atoms away from the active device by one of several methods. One such method is backside damaging of the silicon substrate. By damaging the surface, lattice dislocations form on the backside of the substrate. The metal atoms migrate to the lattice dislocations where they are trapped. Unfortunately, damaging of the backside is usually nonuniform, and tends to cause contamination of the substrate surface by permitting free silicon particles to accumulate at the surface of the substrate.
The depositing of a polysilicon layer onto the backside of the substrate is another method of gettering metal atoms. By forming a layer of polysilicon adjacent to the silicon surface, dislocations of the lattice structure form at the interface of the layers and capture metal molecules from the silicon substrate. Metal atoms will also be trapped at the polysilicon grain boundries. This deposition is costly and time consuming because it requires an additional processing step of depositing a polysilicon layer. Additionally, it has been found that the polysilicon layer is easily etched away which ultimately results in the removal of the gettering material.
A need has therefore arisen for an improved gettering process which eliminates detrimental effects of metal atoms which can migrate to the active device during manufacturing to form a final integrated circuit product. Additionally, there is a need for a gettering process which will not contaminate the surface of a silicon substrate, and which will be evenly deposited to insure efficient gettering of the metal atoms in the substrate. Finally, there is a need for a gettering technique which is easily manufactured and can provide payback.